The present invention relates to systems for filtering electrical signals to remove interference and more particularly to systems for cancelling large amplitude disturbance events contaminating bar code signals.
Certain types of information signals such as the signals generated by bar code readers containing bar code information are characterized by noise containing occasional large amplitude disturbances which may interfere with the processing of these signals. In the past these disturbance events have been controlled by limiting signal amplitude to a maximum as a function of saturation effects whereby excursions are "truncated" at a fixed amplitude level. This approach is generally effective, however, the disturbance events still contaminate the signal even if they now have controlled amplitude. Therefore, these events can still cause problems such as overcompensation by gain control circuitry and excessive threshold elevation in threshold detection systems.
It is therefore an object of the present invention to provide a system for fully cancelling large scale disturbance events so that they do not contaminate information containing signals such as bar code signals.
It is another object of the present invention to provide a filter system which may be implemented in a bar code reader for cancelling disturbance events which would otherwise adversely affect automatic gain control functions.
It is a further object of the present invention to provide a filter system which may be implemented in a bar code reader for cancelling disturbance events which would otherwise adversely affect threshold detection operations.
It is yet another object of the present invention to provide a system for cancelling disturbance events contaminating information signals which is of simple design, is inexpensive to construct and is reliable in operation.